DIY Tube Amp sounds better than a normal Amp?!

I feel like a lot of tube amp lovers hate me because a while ago I did a video about tube amps in which I summarized that they are inefficient and add distortion to the amplified audio signal. No don't get me wrong, I still stand by my words but I also feel like I have done injustice to tube amp enthusiasts. The reason is the commercial tube amp I featured in the video which only uses a vacuum tube for pre-amplification. That of course summoned the pitchfork wielding tube amp lovers and they all said that I should have a look at a real tube amplifier which comes with tubes for its output stage as well as a transformer for driving the speaker. But after finding out what commercial guitar tube amplifier can cost, I thought to myself let's rather DIY one. So I got myself the required vacuum tubes and in this video I will not only show you how I came up with and build a proper tube amp, but I will also directly compare it to a similar transistor amplifier in order to show you the audio differences between them by hearing and also with a bit more scientific method. Let's get started! This video is sponsored by Altium. If you are looking for a professional PCB designer software that can fulfill all your PCB design wishes then look no further than the Altium designer software. After getting used to it, it offers pretty much everything you could ever need when it comes to designing a PCB. So feel free to test the Altium Designer by yourself by following the link in the video description. First off let's have a look at the two tubes that I got. The first one is an ECC83S which is basically the same as the popular 12AX7. It is a triod whose internal structure looks like this. Like mentioned in the previous tube amp video, its control grid is used in order to modulate an electron flow going from the cathode to the anode and therefore amplifying our audio signal. But when looking at the current ratings for this tube, it is clear that it is only useful for pre-amplification and not driving a speaker directly. For that we got this big boy tube which in my case is the 6L6GC. It can handle way higher current and power values and thus should be capable of driving a speaker. But what stood out to me was that this is no longer a triode but instead a pentode whose internal structure look like this. To explain its differences to a triode though it is easier to firstly look at a tetrode which comes with only one additional grid layer. It is called screen grid and to it we can apply a slightly lower but still high voltage in comparison to the anode. Since this grid is closer to the cathode than the anode, it accelerates the electrons better and thus more of them can move to the anode faster. Only problem is that due to this high speed some electrons bounce back from the anode and thus are pretty much wasted. That is why a pentode adds a third suppressor grid which let's the bounced back electrons return to the cathode. So the whole point of this vacuum tube improvement over the years is to basically achieve a higher gain aka a higher amplification factor. And with that in mind I tried coming up with my own tube amp design but I was not 100% sure about every design choice since I never build such an amp before. I knew that it would have to be similar to a class A transistor amplifier which I showed you how to make in a previous video but I was very skeptical about my chosen passive component values. So instead I had a look at a Fender Champ-Amp schematic that you can easily find on the internet and used that as a reference in order to come up with my own modified schematic which was also made possible by helpful feedback from viewers through Twitter, Facebook and Patreon. Ok, as you can see power is provided by the mains grid which I galvanically isolated from the grid with the help of an isolation transformer. And even though such a transformer does offer a bit more safety than usual I have to warn you that working with mains voltage can lead to major injuries if not handled correctly. But anyway, next the AC voltage gets rectified to 325V DC for the power tube and then lowered a bit twice through the help of resistors in order to power the screen of the pentode as well as the complete pre-amplifier section. And like previously mentioned this whole design is very similar to that of a class A transistor amp except of course the transformer part. It is used to convert our high voltage low current signal into a low voltage high current signal for the speaker and thus we would have to perfectly match is impedance. So I want to apologize at this point because my options for suitable transformers were pretty limited and thus it will later not be the perfect fit. But anyway with this schematic in mind it was time to solder all of the components to a perfboard and connect them to one another. And here is something I messed up as well because while I was able to get the correct socket for the big tube, I stupidly ordered the wrong socket for the small tube so I basically had not other choice then to directly solder the small tube to the perfboard. Last but not least I have to say that this is by far my wildest perfboard circuit ever because I had components on both sides and thus it was a bit confusing which pin to connect where. But nevertheless after 3 hours of soldering, my tube amp was done. So I hooked my waveform generator up to its audio input, connected the heating filament to 6.3V DC of my lab bench power supply, connected a 230V 13.5V transformer between the amp and a big speaker and finally connected the power input to my isolating transformer. No, no, I can't do it! What if the design does not make any sense and everything just blows up. No, let's rather try it with my autotransformer here whose output voltage I can slowly crank up. And as a side note, I also added my energy multimeter in series to the amp in order to monitor the voltage and current. OK here we go we are at 15V 3.5mA and it seems like there is no short circuit. OK , right now we are at 40V with 15mA and I hope you can hear this because right now we're getting quite a loud sine wave sound coming from the speaker, awesome. Yep, it seems like the amp works just fine, let's do some testing. Before that though I would like to mention that the amp worked perfectly fine with high voltage values. Now for a comparison I will be using this DIY transistor class A amp which dues to its power rating might not be able to directly power a speaker but we can surely capture is amplified waveform in order to compare it to the output of the tube amp. So let me hook up my guitar and listen to this first sample amplified by transistors. And here is the same track amplified by vacuum tubes. Now It is clear that both audio recordings feature different characteristics and some might like the first one and others the second one but let's face it the question what sounds better is completely subjective so both answers are completely fine. But if we get scientific and for example inject a 1kHz sine wave into both amplifier types then we can see with the help of an FFT, that the tube amp comes with lots of higher frequency harmonics which are the distortions I talked about at the beginning. The transistor amplifier on the other hand features way less of those harmonics. At this point we could also do a Bode-diagram for both amps in order to find out that their gain curve is pretty flat but I do not want to get too technical now. Because in the end it is all about preferences and if you love hearing tube amps then go for it but for me they waste too much power and thus I will stick to my transistor amps. However I have to admit that they sound pretty cool and unique when overdriven so I will give them that. Anyway I hope you learned something through this video. As always consider supporting me through Patreon if you enjoyed this video and want me to produce more. Don't forget to like, share, subscribe and hit the notification bell. Stay creative and I will see you next time.

Channel: GreatScott!

Views: 195,798

Keywords: diy, tube, vacuum, amp, amplifier, audio, sound, guitar, do, it, yourself, make, transistor, class, class a, vs, VS, versus, compare, comparison, difference, quality, project, guide, beginner, beginners, schematic, fender, record, hear, 12ax7, ecc83s, socket, 6l6gc, transformer, output, pre, cathode, anode, grid, triode, pentode, tetrode, control, theory, explain, screen, suppressor, design, greatscott, greatscott!, isolation, variable, test, perfboard, impedance, solder, measure, fft, fourier, bode, plot, fast, transformation, dB, overdrive

Id: 6SFJdovlBMQ

Length: 10min 16sec (616 seconds)

Published: Sun Aug 15 2021

Reddit Comments

[u/Sonnysdad]

Tubes add distortion to the audio signal... say it isn't true !!!

[u/LilPimpinJoe]

I remember reading his Twitter thread live, and lots of people were warning him off using a non-air gapped, repurposed power trafo for the output. Not sure how this circuit is expected to give tube amplification a fair shake given that there was zero optimization done in terms of quiescent current, anode load, or parts selection. Feels like more confirmation bias (can’t argue about the efficiency, though), but a fun exercise nonetheless.